The hip joint includes an acetabulum and a femur which fit together in such a way that enables rotation at the joint. In particular, the head of the femur fits within the acetabulum to form the “ball in socket” joint at the hip. In total hip arthroplasty, both the acetabular side and the femoral side of the hip joint are replaced with prosthetic devices. The prosthetic device used on the acetabular side includes a cup constructed of a ceramic or an alloy including, for example, titanium and/or cobalt-chromium. The prosthetic device used on the acetabular side also includes a cup liner affixed to the concave surface of the cup in a substantially concentric configuration. The liner is provided to reduce friction between the acetabular cup and the head or “ball” of the femoral prosthesis and to improve retention of the head within the cup.
Liners are constructed from a polymer such as, for example, ultra-high-molecular-weight-polyethylene (UHMWPE) or from a metal or an alloy. Materials are chosen to balance wear resistance and fatigue fracture during use within the patient's body. In use, liners have inherent potential for failure in a variety of ways. First of all, the pressures and forces applied to the prosthesis within the hip joint can cause a liner to crack or fracture due to the material properties of the liner. Secondly, if a liner is improperly sterilized prior to implantation, the patient's hip can become infected. Thirdly, a liner can be seated poorly during placement within the implanted cup which can later cause the liner to dislocate or slip out of position during use. Fourthly, a liner can include a manufacturing flaw causing the surface of the liner to be too rough. In this instance, rather than passing smoothly over the surface of the head of the femoral prosthesis, the liner will then adhere to the surface and wear due to the increased adhesive contact. After bearing weight repeatedly on the adhered surface, particles of the liner can break off the liner and be released into the patient's body causing more surface damage to the liner or causing infection. Finally, once a portion of the liner begins to wear, the liner can become delaminated, exacerbating the wear.
Once a liner fails, it is removed from the patient to prevent further trauma and is replaced with a functioning liner to restore functionality. Removing and replacing part of a hip prosthesis is called hip revision arthroplasty. For the purposes of surgical procedures, such as a hip revision arthroplasty, positions and directions relative to surgical instruments may be described using anatomical directions with reference to the physician using the instrument. Accordingly, as used herein, proximal refers to the longitudinal direction of the instrument toward the user/physician when the instrument is in use and distal refers to the longitudinal direction of the instrument away from the user/physician when the instrument is in use. Additionally, inward refers to the direction of the instrument toward the longitudinal axis of the instrument and outward refers to the direction of the instrument away from the longitudinal axis of the instrument.
When performing surgical procedures such as hip revision arthroplasty, physicians generally attempt to damage as little tissue as possible to minimize further trauma to the patient reducing time and effort required for the patient's recovery. Accordingly, if only the liner of the hip prosthesis requires replacement, it is undesirable to remove the cup as well. To facilitate this goal, surgical procedures and instrumentation have been developed which enable separation and removal of the liner from the acetabular cup during hip revision arthroplasty.
Some acetabular prostheses include a locking mechanism to retain the liner within the cup. Removing liners from such prostheses requires using company and/or device specific removal instruments to disengage the locking mechanism. Using company and/or device specific removal instruments increases the number of specific parts and instruments required for the procedure, thus increasing instrumentation costs. Additionally, using company and/or device specific removal instruments increases the time and precision necessary for the procedure due to accurate alignment of particular elements and performance of particular methods to disengage particular features.
In acetabular prostheses that do not include locking mechanisms, liners can be removed by levering out the liners from the acetabular cups with osteotomes. Osteotomes are sharp cutting and chiseling tools used to cut and separate bones. To remove liners using osteotomes, sharp points of the osteotomes are inserted between the cups and the liners. The osteotomes are then levered against the cups to pop the liners out. Using osteotomes to remove liners increases the time and precision necessary for the procedure due to precise placement and manipulation of sharp cutting tools. Additionally, using osteotomes to remove liners employs blunt force and tools which are not necessarily specially adapted to the goal, introducing risks for error. For example, using osteotomes to remove liners potentially results in inadvertent cutting or slicing off parts of the liners which are then loose in the surgical environment.
Another way to remove liners from acetabular prostheses that do not include locking mechanisms is to drill a hole in the liner with a cortical screw and subsequently insert a cancellous screw having a larger diameter than the cortical screw into the drilled hole. The cancellous screw engages the liner along the sides of the drilled hole and the liner is then pulled apart from the acetabular cup by pulling outwardly on the cancellous screw. Using cortical and cancellous screws to remove liners increases the time and precision necessary for the procedure due to precise placement and manipulation of the screws and the drill. Additionally, using cortical and cancellous screws to remove liners employs and tools which are not necessarily specially adapted to the goal, introducing risks for error. For example, using cortical and cancellous screws to remove liners potentially results in drilling the holes into the liners at unfavorable angles which then requires more time to drill a new hole and/or further damages the prosthesis.
Given the above discussion, it would be advantageous to provide an improved acetabular cup liner removal tool including features enabling removal of an acetabular liner from an acetabular cup that is implanted in a patient's acetabulum with greater efficiency and requiring fewer, easier to use tools.